Liquid developing agent and process for producing the same

ABSTRACT

A liquid developing agent for electrophotography or electrostatic recording that can realize a high solid content and has excellent developing properties is characterized in that colored chips produced by heat kneading a pigment with a thermoplastic resin are dispersed by wet pulverization in an electrically insulating hydrocarbon solvent containing at least one pigment dispersant selected from the group consisting of specific modified novolak resins (A) having an aromatic ring and a ring opened structure of an epoxy group by a hydroxycarboxylic acid-derived carboxyl group, and copolymers (B).

RELATED APPLICATION

This is a U.S. national phase patent application under 35 U.S.C. §371 ofInternational Application No. PCT/JP2006/310311 filed May 24, 2006,which claims priority of Japanese Patent Application No. 2005-154073filed May 26, 2005.

TECHNICAL FIELD

The present invention relates to a liquid developing agent forelectrophotography and electrostatic recording used in a printingmachine, copier, printer, and facsimile.

BACKGROUND ART

Liquid developing agents for electrophotography and electrostaticrecording used in a copier, printer, and facsimile are broadlyclassified into a dry developing agent and a liquid developing agent,and it is thought that particle diameter of toner particle is smaller ina liquid developing agent, which is greatly advantageous to obtain ahigh quality photographic image. From this reason, in market there havebeen required liquid developing agents capable of forming a high qualityphotographic image with high image density and low fogging.

As liquid developing agents, generally, toner particles that colorantssuch as pigment covered with thermoplastic resins are dispersed in anelectrically insulating solvent have been used.

As one of relatively easy production methods for obtaining the liquiddeveloping agent, there is proposed a process for producing a liquiddeveloping agent by a wet pulverization method that a colorant and aresin are kneaded by a kneading machine such as a kneader and three-rollmill while heating at a temperature of at least a melting point of theresin, after cooling, the resultant mixture is subjected to drypulverization, the pulverized powder is subjected to wet pulverizationusing a dispersant and electrically insulating nonaqueous solvent togive a concentrated solution of toner, further, dispersed in anelectrically insulating nonaqueous solvent containing a chargecontrolling agent to produce a liquid developing agent (see, e.g.,Japanese Unexamined Patent Publication No. 60-021056A and JapaneseUnexamined Patent Publication No. 05-134468A.

In recent years, however, from the points of higher developing speed,mileage and recovery of electrically insulating solvents, requirementson further high solid content of liquid developing agent have been done,but in the above-described method, it is fundamentally difficult tomaintain dispersion stability and charging characteristics sufficiently,thus there has had a problem that increase in viscosity and lowering ofelectric resistance occur with increase in the solid contentconcentration of a liquid developing agent.

DISCLOSURE OF INVENTION

In this situation, it is an object of the present invention to provide aliquid developing agent that can realize a high solid content and hasexcellent developing properties, and a process for producing the same.

The present inventors have keenly studied to solve the above-describedproblems, as a result, have found the knowledge that can solve all theproblems and completed the present invention as follows: a pigment andthermoplastic resin are heat kneaded, then further, which is subjectedto wet pulverization in an electrically insulating hydrocarbon solventcontaining a specific pigment dispersant having an aromatic ring and aring-opened structure of an epoxy group by a hydroxycarboxylicacid-derived carboxyl group to produce a liquid developing agent.

Namely, the present invention provides the following liquid developingagent and a process for producing the same.

[1] A liquid developing agent where a colored chip obtained by heatkneading a pigment with a thermoplastic resin is dispersed by wetpulverization in an electrically insulating hydrocarbon solventdispersing at least one pigment dispersant selected from the groupconsisting of the following modified novolak resin (A) and a copolymer(B) having an aromatic ring and a ring-opened structure of an epoxygroup by a hydroxycarboxylic acid-derived carboxyl group:

Modified novolak resin (A): a modified novolak resin having a novolakresin-derived aromatic ring and at least one group shown by a generalformula (1) by ring-opening of an epoxy group by a hydroxycarboxylicacid-derived carboxyl group:

wherein an oxygen atom at the far left is derived from an oxygen atomcontained in an aromatic hydroxyl group of a novolak resin, W¹ and X¹each independently represent a divalent hydrocarbon group with carbonnumbers of 1 to 19, i and j each independently represent an integer ofi=1 to 30 and j=0 to 30, and R¹ represents a hydrogen atom or a methylgroup.Copolymer (B): a copolymer with a weight-average molecular weight of3000 to 100000, having, in said copolymer, the amount corresponding toat least 10 mol % of the recurring unit shown by a general formula (2),and the amount corresponding to at least 10 mol % of at least one kindselected from the recurring units shown by a general formula (3) and ageneral formula (4)

wherein W² and X² each independently represent a divalent hydrocarbongroup with carbon numbers of 1 to 19, p and q each independentlyrepresent an integer of p=1 to 30, and q=0 to 30, R², R³ and R⁴ eachindependently represent a hydrogen atom or a methyl group, R⁵ representsa hydrogen atom or a halogen atom, R⁶ and R⁷ each independentlyrepresent a hydrogen atom, a hydrocarbon group with carbon numbers of 1to 5, an alkoxy group with carbon numbers of 1 to 5, an aryloxy groupwith carbon numbers of 6 to 10, or a halogen atom, R⁸ represents ahydrogen atom or a methyl group, and R⁹ represents a direct bond or amethylene group.

[2] The liquid developing agent described in the [1], wherein theconcentration of the total solid content in a liquid developing agentwas 13 to 50% by mass.

[3] The liquid developing agent described in the [1] or [2], wherein thecomposition of the pigment dispersant is 2 to 100 parts by mass relativeto 100 parts by mass of the colored chip.

[4] The liquid developing agent described in any one of the [1] to [3],wherein said electrically insulating hydrocarbon solvent is a highboiling point paraffin solvent.

[5] A process for producing the liquid developing agent described in anyone of the [1] to [4], wherein the colored chip obtained by heatkneading a pigment with a thermoplastic resin is subjected to drypulverization into a coarse pulverized powder beforehand, further, saidpulverized powder is subjected to wet pulverization in an electricallyinsulating hydrocarbon solvent dissolving at least one pigmentdispersant selected from the group consisting of said modified novolakresin (A) and said copolymer (B).

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below.

First, constituent materials used in the liquid developing agent of thepresent invention are explained.

As the pigment used in the present invention, inorganic pigments andorganic pigments conventionally used in a liquid developing agent can beused without limitation in particular, for example, there are listedinorganic pigments such as carbon black including acetylene black;graphite, colcothar, chrome yellow and ultramarine blue; and organicpigments such as azo pigments, condensed azo pigments, lake pigments,phthalocyanine pigments, isoindoline pigments, anthraquinone pigmentsand quinacridone pigments. Regarding various kinds of hues of organicpigments, as magenta-type organic pigments, there are listedquinacridone pigments such as quinacridone red; azo pigments such aspermanent red; condensed azo pigments such as condensed azo red, andperylene pigments such as perylene red. As cyanogen-type pigments,phthalocyanine pigments such as metal-free phthalocyanine blue,phthalocyanine blue and fast sky blue are listed. As yellow-type organicpigments, there are listed monoazo pigments such as hansa yellow, disazopigments such as benzine yellow and permanent yellow; and condensed azopigments such as condensed azo yellow. As green-type pigments,phthalocyanine pigments such as phthalocyanine green are listed. Thesepigments can be used alone or in mixture of at least 2 kinds thereof.

The content of pigment in a liquid developing agent is not particularlylimited, it is preferably 1 to 20 parts by mass in the 100 parts by massof final liquid developing agent from the point of image density.

As a thermoplastic resin used in the present invention, knownthermoplastic resins used in a liquid developing agent can be adopted,which are insoluble in an electrically insulating hydrocarbon solvent,preferably have a low degree of swelling to electrically insulatinghydrocarbon solvents. When the degree of swelling of thermoplastic resinis high, it is difficult to realize a high solid content, which tends topose a problem that flogging and stain in non-image part of photographicimage take place when developing speed is increased.

The thermoplastic resins include, for example, synthetic resins ornatural resins such as a polyester resin, epoxy resin, acryl resin,styrene resin, styrene-acryl copolymer resin, polyvinylchloride resin,polyvinyl acetate resin, polyethylene resin, polypropylene resin,polyurethane resin, polyvinyl butyral resin, rosin resin, modified rosinresin, terpene resin, phenol resin, aliphatic hydrocarbon resin andaromatic petroleum resin. These thermoplastic resins can be used aloneor in mixture of at least 2 kinds thereof.

Additionally the ratio of the sum of pigment and thermoplastic resin inthe liquid developing agent of the present invention is preferably 10 to50% by mass, more preferably 15 to 40% by mass. When the ratio of thesum of pigment and thermoplastic resin is less than the above-describedrange, there is an instance that a sufficient concentration is notobtained as a liquid developing agent, when more than theabove-described range, there is an instance that a problem of excessincrease in viscosity of liquid developing agent is posed.

As the electrically insulating hydrocarbon solvent used in the presentinvention, it is a solvent which does not solve the above-describedthermoplastic resin, there can be used one with a volume resistivity(about 10¹¹ to 10¹⁶ Ω·cm) not disturbing electrostatic latent image,such as an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatichydrocarbon and a halogenated hydrocarbon. Among them, from theviewpoints of odor, non-toxicity and cost, preferable are paraffinsolvents with a high boiling point (boiling point of at least 150° C.under normal pressure) such as n-paraffin solvents, isoparaffin solventsand cycloparaffin solvents, or a mixture of at least 2 kinds thereof. Ascommercial products of n-paraffin solvents, isoparaffin solvents,cycloparaffin solvents or a mixture thereof, for example, preferableones are Isopar G. Isopar H, Isopar L. Isopar M and Exxsol D130, andExxsol D140 (all of them, manufactured by Exxon Chemical Corporation),Shellsol 71 (manufactured by Shell Sekiyu K.K.), IP Solvent 1620, IPSolvent 2080 and IP Solvent 2835 (all of them, manufactured by IdemitsuKosan Co., Ltd.), Moresco White P-40, Moresco White P-55 and MorescoWhite P-80 (all of them, manufactured by Matsumura oil Co., Ltd.),Liquid paraffin No. 40-S and Liquid paraffin No. 55-S (all of them,manufactured by Chuokasei Co., Ltd.).

The pigment dispersant used in the present invention is at least onepigment dispersant selected from the group consisting of theabove-described modified novolak resin (A) and copolymer (B), which issolved in an electrically insulating hydrocarbon solvent.

Additionally, the above-described copolymer (B) has a relatively largeside chain shown by the general formula (2) hanging down from the mainchain, and such structure is observed in a graft copolymer. From suchpoint, the copolymer (B) is referred to as graft copolymer (B) in thepresent specification.

First, the above-described modified novolak resin (A) is explained.

As a novolak resin to obtain the modified novolak resin (A), a novolakresin which is derived from monovalent phenols or multivalent phenolssuch as di or trioxybenzene and aldehydes can be used. As the monovalentphenols, there can be used unsubstituted phenols or alkyl-substitutedphenols such as phenol, cresol, xylenol, trimethylphenol, propylphenol,butylphenol, amylphenol, hexylphenol, octylphenol, nonylphenol anddodecylphenol; or phenols having aromatic substituents such asmonohydroxydiphenylmethane and phenylphenol. As the multivalent phenols,di or trihydroxybenzenes such as catechol, resorcinol, hydroquinone andtrihydroxybenzene; or the alkyl-substituted or aromatic-substituted onesthereof. Further, dihydroxydiphenylmethanes of bisphenol A or bisphenolF, and dihydroxybiphenyls can also be used. Halogen-substituted phenolsof the above-described phenols can also be used, for example,chlorinated or brominated phenols can be listed. These phenols can beused alone or in mixture of at least 2 kinds thereof.

Regarding the phenols, from the point of reactivity, phenols substitutedby one alkyl group at the meta position are preferable as monovalentphenols, and resorcinol is preferable as multivalent phenols.

As aldehydes, one used generally in production of a novolak resin can beused without limitation in particular. Specifically, there are listedlower aliphatic aldehydes such as formaldehyde, paraformaldehyde,trioxane, cyclic formals, acetaldehyde, propionaldehyde,n-butylaldehyde, isobutylaldehyde and glyoxal; and aromatic aldehydessuch as furfural and phenylaldehyde. These aldehydes can be used aloneor in mixture of at least 2 kinds thereof.

To synthesize a novolak resin, according to a common method, thesephenols and aldehydes may be reacted at 80 to 130° C. in the presence ofan acid catalyst such as p-toluenesulfonic acid, perchloric acid,hydrochloric acid, nitric acid, sulfuric acid, chloroacetic acid, oxalicacid and phosphoric acid. The reaction can be traced by a gel permeationchromatography (GPC) through measuring molecular weights.

Other than this method, a novolak resin may be synthesized by a methodusing a phenol derivative having a hydroxymethyl group like saligenin,or phenol derivative having a halogenated methyl group likeo-chloromethylphenol.

Next, according to a common method, a novolak resin is reacted withepichlorohydrin or β-methylepichlorohydrin to obtain a novolak resinhaving an epoxy group. Obviously, a commercial novolak resin having anepoxy group can also be used.

Finally, a target modified novolak resin (A) is obtained by reacting anovolak resin having an epoxy group with carboxylic acids or aminesdescribed later. This reaction may use a solvent if necessary, use acatalyst such as an aliphatic amine, an aromatic amine and ammonium saltif necessary, and it can be carried out by heating at 60 to 160° C. Theprogress of reaction can be traced by GPC through measuring molecularweights or by measuring epoxy equivalents.

As described above, in addition to a method that modification is carriedout after synthesis of a novolak resin, first, an aromatic hydroxylgroup of the foregoing monovalent phenol or multivalent phenol isreacted with epichlorohydrin or β-methylepichlorohydrin to form aglycidyloxy group or 2,3-epoxy-2-methylpropyloxy group, which is reactedwith carboxylic acids or amines described later, new phenols are addedthereto if necessary, which is subjected to novolak resinificationreaction using aldehydes, thereby a modified novolak resin (A) can beobtained.

A group shown by the general formula (1) in a modified novolak resin (A)can be obtained by reacting an aromatic hydroxyl group withepichlorohydrin or β-methylepichlorohydrin, then, by reacting theresultant product with a hydroxycarboxylic acid of carbon numbers of 2to 20 that may have an unsaturated bond or a branched structure, or themixture thereof or the polycondensate thereof.

In the general formula (1), an oxygen atom at the far left is derivedfrom an oxygen atom contained in an aromatic hydroxyl group of a novolakresin, W¹ and X¹ represent a divalent hydrocarbon group with carbonnumbers in a range of 1 to 19 that may have an unsaturated bond and/or abranched structure, and R¹ represents a hydrogen atom or a methyl group.

In the general formula (1), a general formula (5):

wherein W¹ and i are the same as described above, and a general formula(6):

wherein X¹ and j are the same as described above, these groups can bederived from a hydroxycarboxylic acid with carbon numbers in a range of2 to 20 that may have an unsaturated bond and/or a branched structure,or the mixture thereof or the polycondensate thereof.

As the above-described hydroxycarboxylic acid, there are listed glycolicacid, lactic acid, oxybutyric acid, hydroxyvaleric acid, hydroxycaproicacid, hydroxycaprylic acid, hydroxycaproic acid, hydroxylauric acid,hydroxymyristic acid, hydroxypalmitic acid, ricinoleic acid, caster oilfatty acid, and their hydrogenated products and 12-hydroxystearic acid.Above all, hydroxycarboxylic acid with carbon numbers in a range of 12to 20 is preferred, particularly preferably, hydroxycarboxylic acid withcarbon numbers in a range of 16 to 20 such as ricinoleic acid, casteroil fatty acid, and their hydrogenated products, and 12-hydroxystearicacid can be preferably used.

Repeating number i represents an integer in a range of 1 to 30, and jrepresents an integer in a range of 1 to 30. However, a suitable valuedepends on the kind of pigment used, specific surface area and particlediameter of pigment particle, properties of pigment surface treatingagent, the kind of thermoplastic resin, and polarity of dispersant, itneeds to select the optimum value according to each case. However,generally, i or j≧2, and I+j≧2 are preferred. When i or j exceeds theabove-described range, dispersibility cannot be improved any more.

In the general formula (1), formation of a group shown by the generalequation (5) or the general formula (6), for example, can be made by amethod that a polyester is synthesized by polycondensation of ahydroxycarboxylic acid beforehand, and the terminal carboxylic group isreacted with the aforementioned epoxy group; or by a method that acarboxyl group of a hydroxycarboxylic acid is reacted with theaforementioned epoxy group, then further, the hydroxycarboxylic acid ispolycondensated.

The above-described polycondensation reaction of the hydroxycarboxylicacid can be done by heating a reaction system at 180 to 220° C. andstirring in the presence of, or without the presence of a catalyst suchas p-toluenesulfonic acid, stannous octylate, dibutyltin diacetate, andtetra-n-butyl titanate, while water generated is removed by azeotropicsolvents such as toluene and xylene. The reaction can be traced by GPCthrough measuring molecular weights or by measuring acid values.

The modified novolak resin (A) must have a group shown by the generalformula (1) in a molecule. The number of the groups in the generalformula (1) is preferably 1 to 20. A sufficient dispersion is notobtained when there is no this group. When the number of the groupsexceeds the above-described range, although the effect can be attained,it becomes very difficult to control the molecular weight of a novolakresin having a larger number of a phenolic ring necessary for that, sothat 20 is practically an upper limit. However, a suitable value dependson the kind of pigment used, specific surface area and particle diameterof pigment particle, presence or property of pigment surface treatingagent, the kind of thermoplastic resin, and polarity of dispersant, itneeds to select the optimum value according to application.

Moreover, the modified novolak resin (A) may further have in a moleculea group shown by a general formula (7):

wherein an oxygen atom at the far left is derived from an oxygen atomcontained in an aromatic hydroxyl group of a novolak resin, Y representsa monovalent organic group with carbon numbers in a range of 1 to 20having an oxygen atom or a nitrogen atom at the terminal position(except the group shown by the general formula (5)) and R¹⁰ represents ahydrogen atom or a methyl group.

The group shown by the general formula (7) can be obtained by reactingan aromatic hydroxyl group with epichlorohydrin orβ-methylepichlorohydrin, followed by reacting with monovalent carboxylicacids or monovalent amines. Additionally, a basic group formed by thereacting monovalent amines tends to affect an adverse influence oncharging characteristics, hence, it is preferable not to use monovalentamines. In the case of using monovalent amines, it is necessary to payattention on the amount used.

As concrete examples of the monovalent carboxylic acids, there can beused saturated acids such as acetic acid, propionic acid, butyric acid,caproic acid, caprylic acid, capric acid, lauric acid, myristic acid,palmitic acid and stearic acid; unsaturated acids such as oleic acid,elaidic acid, linoleic acid, linolenic acid, arachidonic acid andeleostearic acid; and their hydrogenated acids.

As the monovalent amines, there can be used aliphatic primary monoaminessuch as methylamine, ethylamine, propylamine, butylamine, amylamine,octylamine, dodecylamine, stearylamine and benzylamine; aromatic primarymonoamines such as aniline and naphthylamine, and theirN-monoalkyl-substituted secondary monoamines; alkanol monoamines havinga primary or secondary amino group such as ethanolamine,N-monoalkylethanolamine and diethanolamine.

Moreover, the modified novolak resin (A) may further have in a moleculea group shown by a general formula (8) and an aromatic hydroxyl group:

wherein an oxygen atom at the far left is derived from an oxygen atomcontained in an aromatic hydroxyl group of a novolak resin, and R¹²represents a hydrogen atom or a methyl group.

This means that a glycidyloxy group, 2,3-epoxy-2-methylpropyloxy groupor aromatic hydroxyl group may be remained. However, it is notpreferable for a modified novolak resin (A) to have both the group shownby the general formula (8) and an aromatic hydroxyl group. When itcontains both, there is a tendency of generating gel.

There is no problem when the number of groups of a group shown by thegeneral formula (7), a group shown by the general formula (8) and anaromatic hydroxyl group is each in a range of 0 to 19. When it exceedsthis range, although the effect is attained, from the points that itbecomes very difficult to control the molecular weight of a novolakresin with large functional group number and also at least one groupshown by the general formula (1) must be present, 19 is practically therespective upper limits. However, a suitable value depends on the kindof pigment used, specific surface area and particle diameter of pigmentparticle, presence or property of pigment surface treating agent, thekind of thermoplastic resin, and polarity of dispersant, it ispreferable to select the optimum value according to application.

The modified novolak resin (A) may be further substituted with acrosslinking group intermolecular or within a molecule shown by ageneral formula (9):

wherein an oxygen atom at the far right is derived from an oxygen atomcontained in an aromatic hydroxyl group of the same molecule ordifferent molecules of a novolak resin, Z represents an organic group of2 to 6 functionalities with carbon numbers in a range of 1 to 40 havingan oxygen atom or nitrogen atom at the terminal position, k representsan integer in a range of 2 to 6, and R¹¹ represents a hydrogen atom or amethyl group.

To substitute an active hydrogen of an aromatic hydroxyl group by acrosslinking group intermolecular or within a molecule shown by thegeneral formula (9), an aromatic hydroxyl group may be reacted withepichlorohydrin or β-methylepichlorohydrin, thereafter, which may bereacted with carboxylic acids of 2 to 6 functionalities, amines(including primary monoamine) or amino acids. Additionally, since abasic group formed by reacting amines or amino acids tends to affect anadverse influence on charging characteristics, it is preferable not touse amines or amino acids. In the case of using amines or amino acids,it is necessary to pay attention to the amount used.

As concrete examples of the multifunctional carboxylic acid, there canbe used aliphatic polycarboxylic acids such as succinic acid, maleicacid, itaconic acid, cyclohexane dicarboxylic acid, adipic acid, azelaicacid, sebacic acid, 1,10-decanedicarboxylic acid, dodecenylsuccinicacid, dimer acid, 3,6-endomethylenetetrahydrophthalic acid, and3,6-methylendomethylenetetrahydrophthalic acid; and aromaticpolycarboxylic acids such as phthalic acid, isophthalic acid,terephthalic acid, trimellitic acid, pyromellitic acid,benzophenonetetracarboxylic acid, ethyleneglycol bistrimellitate, andglycerol tristrimellitate.

As concrete examples of the multifunctional amines, there are listedethylenediamine, diethylenetriamine, triethylenetetramine,tetraethylenepentamine, pentaethylenehexamine, propylenediamine,(dimethylamino)propylamine, (diethylamino)propylamine,hexamethylenediamine, hexamethylenetriamine,N,N-bis(aminopropyl)methylamine, isophoronediamine, norbornanediamine,diaminodicyclohexylmethane, N-(aminoethyl)piperazine,N,N′-bis(aminoethyl)piperazine, xylylenediamine and dimer diamine; andaromatic polyamines such as melamine, benzoguanamine, m-phenylenediamineand diaminodiphenylmethane.

Further, polyetherdiamine, N-aminoethylethanolamine, or so-calledpolyaminoamide can also be used.

Further, a crosslinked structure can be formed by reacting an epoxygroup with a primary amino group of two functionalities. In this case,the foregoing primary monoamine can also be used.

Amino acids such as leucine and threonine can also be used.

The above-described reaction can be carried out by heating at 60 to 160°C. using a suitable organic solvent if necessary, and using a catalystif necessary such as an aliphatic tertiary amine, an aromatic tertiaryamine and an ammonium salt of a tertiary amine. The progress of reactioncan be traced by GPC through measuring molecular weights or by measuringepoxy equivalents.

It is very difficult to control molecular weight of a novolak resinhaving a larger number of a phenolic ring, so it is preferable that thesum of aromatic hydroxyl groups of a modified novolak resin (sum ofunsubstituted and substituted aromatic hydroxyl groups, the same below)is at most 20.

Next, the above-described graft copolymer (B) is explained.

The graft copolymer (B) can be obtained through reaction in a commonmethod: (I) by using 10 to 90 mol % of an epoxy group-containingethylenically unsaturated monomer shown by a general formula (10):

wherein R² and R³ are the same as described above, and using 10 to 90mol % of a monomer shown by a general formula (11):

wherein R⁴, R⁵, R⁶ and R⁷ are the same as described above, and/or, 10 to90 mol % of a monomer shown by a general formula (12):

wherein R⁸ and R⁹ are the same as described above, according to need,using 0 to 80 mol % of other ethylenically unsaturated monomer having nofunctional group with high reactivity to an epoxy group, and a radicalpolymerization initiator such as peroxide and azo compounds, afterobtaining a copolymer containing an epoxy group is obtained by a commonmethod, followed by reacting an epoxy group of said copolymer with ahydroxycarboxylic acid, if necessary, carboxylic acids and amines; or(II) by using 10 to 90 mol % of a monomer shown by a general formula(13):

wherein R², R³, W² and X² are the same as described above, m and n eachindependently represent an integer of m=1 to 30, n=0 to 30, and ifnecessary, by a general formula (14):

wherein, V is a monovalent organic group with carbon numbers in a rangeof 1 to 20 at the terminal positions, however, excluding the group shownby a general formula (15):

wherein W² and p are the same as described above, R¹³ and R¹⁴ eachindependently represent a hydrogen atom or a methyl group, and using 10to 90 mol % of the monomer shown by the general formula (11) and/or thegeneral formula (12), according to need, using 0 to 80 mol % of otherethylenically unsaturated monomer having no functional group with highreactivity to an epoxy group, and a radical polymerization initiatorsuch as peroxide and azo compound.

Additionally, an epoxy group of the copolymer obtained in theabove-described method (1) is reacted with carboxylic acids or aminesdescribed later; a reaction to obtain a structural unit shown by thegeneral formula (2) and a general formula (16):

wherein V, R¹³ and R¹⁴ are the same as described above, or a reaction toobtain a monomer shown by the general formula (13) and the generalformula (14) by reacting an epoxy group of epoxy group containingethylenically unsaturated monomer shown by the general formula (10) inthe above-described method (II) with a hydroxycarboxylic acid, accordingto need, with carboxylic acids or amines, uses a solvent according toneed, or uses an aliphatic amine, an aromatic amine or an ammonium saltaccording to need, and it can be conducted by heating at 60 to 160° C.

In the recurring unit shown by the above-described general formula (3),a chlorine atom is listed as a halogen atom represented by R⁵. As ahydrocarbon group with carbon number 1 to 5 represented by R⁶ or R⁷, forexample, there are listed alkyl groups such as methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, t-butyl and pentyl; as an alkoxy groupwith carbon numbers of 1 to 5, for example, methoxy and butoxy arelisted, as an aryloxy group with carbon numbers of 6 to 10, for example,phenoxy is listed, and as a halogen atom, for example, a fluorine atom,a chlorine atom and a bromine atom are listed.

Regarding monomers used in production of the graft copolymer (B), asstyrene derivatives among monomers shown by the general formula (11),there can be used an alkyl-substituted styrene such as vinyl toluene,α-methylstyrene, dimethylstyrene, ethylstyrene, isopropylstyrene andt-butylstyrene; a halogen-substituted styrene such as chlorostyrene,dichlorostyrene, bromostyrene and fluorostyrene; an alkoxy-substitutedstyrene such as methoxystyrene and butoxystyrene; an aryloxy-substitutedstyrene such as phenoxystyrene; and β-chlorostyrene.

As the monomer shown by the general formula (12), benzyl (meth)acrylateand phenyl (meth)acrylate are listed.

As the epoxy group containing ethylenically unsaturated monomer shown bythe general formula (10), glycidyl (meth)acrylate, and2,3-epoxy-2-methylpropyl (meth)acrylate can be used.

As other ethylenically unsaturated monomer having no functional groupwith high reactivity to an epoxy group used according to need, there canbe used an ethylenically unsaturated monomer having no functional groupwith high reactivity to an epoxy group such as a carboxyl group, aphenolic hydroxyl group, a primary amine and a secondary amine. Forexample, there can be listed alkyl esters of (meth)acrylic acid such asmethyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, dodecyl(meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, behenyl(meth)acrylate and norbornyl (meth)acrylate; (meth)acrylates having acyclic ether group such as tetrahydrofurfuryl (meth)acrylate;(meth)acrylates having an aliphatic hydroxyl group such as2-hydroxyethyl (meth)acrylate; (meth)acrylates having tertiary aminogroup such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl(meth)acrylate; vinyl ethers such as methyl vinyl ether, dodecyl vinylether and propenyl ether propylene carbonate; vinyl ethers having analiphatic hydroxyl group such as hydroxybutyl vinyl ether; and allylesters of various acids such as allyl acetate.

Additionally, in the case where a graft copolymer is obtained by using amonomer shown by the general formula (13) or the general formula (14)being obtained by reacting an epoxy group containing ethylenicallyunsaturated monomer with a hydroxycarboxylic acid, according to need,with carboxylic acids and amines, there can be used an ethylenicallyunsaturated monomer having a functional group with high reactivity to anepoxy group, such as a carboxyl group, a phenolic hydroxyl group, aprimary amine and a secondary amine.

The recurring unit shown by the general formula (2) in the graftcopolymer (B) can be obtained from a recurring unit derived from anepoxy group containing ethylenically unsaturated monomer shown by theabove-described (10) and a hydroxycarboxylic acid with carbon numberswith 2 to 20 that may have an unsaturated bond or a branched structure,their mixture or the polycondensate. Alternatively, it can be derivedfrom a monomer shown by the general formula (13) obtained from an epoxygroup containing ethylenically unsaturated monomer shown by theabove-described (10) and hydroxycarboxylic acid with carbon numbers with2 to 20 that may have an unsaturated bond or a branched structure, themixture or the polycondensate thereof.

In the general formula (2), W² and X² represent a divalent hydrocarbongroup with carbon numbers in a range of 1 to 19 that may have anunsaturated bond and/or a branched structure, R² and R³ eachindependently represent a hydrogen atom or a methyl group.

In the general formula (2), a group shown by a general formula (15):

wherein W² and p are the same as described above, and by a generalformula (17):

wherein X² and q are the same as described above, can be derived from ahydroxycarboxylic acid with carbon numbers in a range of 2 to 20 thatmay have an unsaturated bond and/or a branched structure, the mixture orthe polycondensate thereof.

As the above-described hydroxycarboxylic acid, there are listed glycolicacid, lactic acid, oxybutyric acid, hydroxyvaleric acid, hydroxycaproicacid, hydroxycaprylic acid, hydroxycaproic acid, hydroxylauric acid,hydroxymyristic acid, hydroxypalmitic acid, ricinoleic acid, caster oilfatty acid, and their hydrogenated products, and 12-hydroxystearic acid.Among them, a hydroxycarboxylic acid with carbon numbers in a range of12 to 20 is preferred, particularly preferably, there can preferablyused hydroxycarboxylic acids with carbon numbers in a rang of 16 to 20such as ricinoleic acid and a caster oil fatty acid and theirhydrogenated products, and 12-hydroxystearic acid.

Repeating number p represents an integer in a range of 1 to 30, and qrepresents an integer in a range of 0 to 30. However, a suitable valuedepends on the kind of pigment used, specific surface area and particlediameter of pigment particle, properties of pigment surface treatingagent, the kind of thermoplastic resin, and polarity of dispersant, itneeds to select the optimum value according to application. However,generally, p or q≧2, and p+q≧2 are preferred. When p or q exceeds theabove-described range, dispersibility cannot be improved any more.

Formation of a group shown by the general formula (15) or the generalformula (17) in the general formula (2) can be done, for example, by amethod that polyester is synthesized beforehand by polycondensation of ahydroxycarboxylic acid, whose terminal carboxyl group is reacted withthe aforementioned epoxy group; or a method that a carboxylic group of ahydroxycarboxylic acid monomer is reacted with the aforementioned epoxygroup, then, further polycondensated with a hydroxycarboxylic acid.

The polycondensation reaction of the above-described hydroxycarboxylicacid can be conducted by heating and stirring a reaction system at 180to 220° C. in the presence or without the presence of a catalyst such asp-toluenesulfonic acid, stannous octylate, dibutyltin diacetate andtetra-n-butyl titanate, while removing water generated by azeotropicsolvents such as toluene and xylene. The reaction can be traced by GPCthrough measuring molecular weights or by measuring acid values.

The graft copolymer (B) must have a recurring unit shown by the generalformula (2) and a recurring unit shown by the general formula (3) and/orthe general formula (4). The content of these relative to the graftcopolymer (B) is preferably the amount corresponding to at least 10 mol% of a recurring unit shown by the general formula (2) in the graftcopolymer (B), above all, the amount corresponding to 10 to 90 mol %;and the amount corresponding to at least 10 mol % of at least one kindselected from recurring units shown by the general formula (3) and thegeneral formula (4), above all, the amount corresponding to 10 to 90 mol%. Additionally, what is meant to contain the amount corresponding to atleast 10 mol % of a recurring unit shown by the general formula (2) isthat a graft copolymer is divided into recurring units derived fromethylenically unsaturated monomers, the recurring unit shown by thegeneral formula (2) contains at least 10 mol % to the whole recurringunits. Namely, in the case where a graft copolymer is obtained bycopolymerization of n ethylenically unsaturated monomers, the number ofrecurring units shown by the general formula (2) in a molecule of saidgraft copolymer means at least 0.1×n. Further, what is meant to containthe amount corresponding to at least 10 mol % of at least one kindselected from recurring units shown by the general formula (3) and thegeneral formula (4) is that a graft copolymer is divided into recurringunits derived from ethylenically unsaturated monomers, at least one kindselected from recurring units shown by the general formula (3) and thegeneral formula (4) contains at least 10 mol %. Namely, in the casewhere a graft copolymer is obtained by copolymerization of nethylenically unsaturated monomers, the number of recurring units of atleast one kind selected from recurring units shown by the generalformula (3) and the general formula (4) means at least 0.1×n.

When either the recurring unit shown by the general formula (2) or atleast one kind of recurring unit selected from recurring units shown bythe general formula (3) and the general formula (4), or both do notcontain the amount corresponding to a predetermined mol, sufficientdispersibility cannot be obtained. However, a suitable value depends onthe kind of pigment used, specific surface area and particle diameter ofpigment particle, presence or property of pigment surface treatingagent, the kind of thermoplastic resin, and polarity of dispersant, itis preferable to select the optimum value according to application.

Further, the graft copolymer (B) may have a recurring unit shown by ageneral formula (16).

The recurring unit shown by the general formula (16) can be obtained byreacting an epoxy group containing ethylenically unsaturated monomer oran epoxy group of copolymer with monovalent carboxylic acids ormonovalent amines. Additionally, a basic group formed by reactingmonovalent amines tends to affect an adverse influence on chargingcharacteristics, hence, it is preferable not to use monovalent amines.In the case of using monovalent amines, it is necessary to pay attentionto the amount used.

As concrete examples of the monovalent carboxylic acids, there can beused saturated fatty acids such as acetic acid, propionic acid, butyricacid, caproic acid, caprylic acid, capric acid, lauric acid, myristicacid, palmitic acid and stearic acid; and unsaturated acids such asoleic acid, elaidic acid, linoleic acid, linolenic acid, arachidonicacid and eleostearic acid.

As the monovalent amines, there can be used aliphatic primary monoaminessuch as methylamine, ethylamine, propylamine, butylamine, amyl amine,octylamine, dodecylamine, stearylamine, benzylamine; aromatic primarymonoamines such as aniline and naphthylamine, and secondary monoaminesof these by N-monoalkyl substitution; and alkanolmonoamines having aprimary or secondary amino group such as ethanolamine,N-monoalkylethanolamine and diethanolamine.

Further, the graft copolymer (B) may have a recurring unit shown by ageneral formula (18):

wherein R¹⁵ and R¹⁶ each independently represent a hydrogen atom or amethyl group.

This means that a glycidyloxy group or a 2,3-epoxy-2-methylpropyloxygroup in an epoxy group containing ethylenically unsaturated monomer mayremain intact.

The above-described graft copolymer (B) has a weight-average molecularweight of 3000 to 100000. When the weight-average molecular weight isless than the above-described range, although dispersibility issufficient, it is difficult to adjust polymerization, whereas when itexceeds the above-described range, sufficient dispersibility tends to bedifficult to obtain.

In the present invention, in a system where an electrically insulatinghydrocarbon solvent is used as a solvent, by using the above-describedspecific pigment dispersant, a liquid developing agent with high solidcontent concentration having excellent dispersion stability andredispersibility can be obtained without lowering the electricresistance value (volume resistivity).

The amount of pigment dispersant used in the present invention ispreferably 2 to 100 parts by mass relative to 100 parts by mass ofcolored chip obtained by heat kneading a pigment with a thermoplasticresin, more preferably 2 to 50 parts by mass. When the amount of pigmentdispersant used is less than the above-described range, dispersibilityand redispersibility tend to be lowered, whereas when it exceeds theabove-described range, electric resistance value tends to be lowered.

As charge controlling agents used in the present invention according toneed, they are broadly classified into two types of (1) and (2) whichwill be explained below.

(1) A type of comprising a substance capable of ionization or absorptionof ion, thereby covering the surface of toner particle:

Preferable charge controlling agents of this type include fat such aslinseed oil and soy oil, alkyd resin, a halogenated polymer, an aromaticpolycarboxylic acid, an acid group-containing aqueous dye, and anoxidized condensate of an aromatic polyamine.

(2) A type of making coexistence by dissolving a substance capable ofgiving and receiving ions with a toner particle in an electricallyinsulating solvent:

Preferable charge controlling agents of this type include metal soapsuch as cobalt naphthenate, nickel naphthenate, iron naphthenate, zincnaphthenate, zirconium octylate, cobalt octylate, nickel octylate, zincoctylate, cobalt dodecanoate, nickel dodecanoate, zinc dodecanoate, andcobalt 2-ethylhexanoate; metal sulfonates such as petroleum metalsulfonate and metal sulfosuccinate; phospholipids such as lecithin andkephalin; metal salicylates such as t-butylsalicylic acid a metalcomplex; a polyvinylpyrolidone resin, a polyamide resin, a sulfonicacid-containing resin and a hydroxybenzoic acid derivative.

Next, a process for producing the liquid developing agent of the presentinvention is explained.

In the present invention, actually as long as a colored chip obtained byheat kneading of pigment and thermoplastic resin is minutely powdered bywet pulverization, and dispersed in an electrically insulating solventcontaining the above-described pigment dispersant, the kind of powderingmachine and dispersing machine, a combination of powdering steps are notparticularly limited. Herein, a simple production method withcombination of both dry pulverization and wet pulverization of coloredchip is explained.

First, the above-described pigment and thermoplastic resin areheat-kneaded by a three-roll mill, and a biaxial extruder, after beingcooled, the resultant colored chip is dry-pulverized by a dry powderingmachine. The coarse pulverized powder obtained by dry pulverization haspreferably an average particle diameter of about 7 to 12 μm.Additionally, when the kneaded product subjected to dry pulverization issoft, for example, in the case of softening point of at most 100° C., itis cooled and embrittled with liquid nitrogen or solid carbon dioxidebefore pulverization. As the dry powdering machine, for example, therecan be optionally used a hammer mill, a jet mill, a pin mill, aturbomill, a cutter mill and a ball mill.

Next, using a wet powdering machine, the above-described coarsepulverized powder by dry pulverization is subjected to wet pulverizationin an electrically insulating solvent containing at least one pigmentdispersant selected from the foregoing modified novolak resin (A) andthe foregoing graft copolymer (B), the liquid developing agent of thepresent invention can be obtained thereby. Additionally, a chargecontrolling agent that can be added according to need may be added uponwet pulverization and/or after wet pulverization. As the above-describedpowdering machine, for example, there can be optionally used media-typepowdering machines such as an Eiger mill, an atoreiter, a sand mill, adinomill, a ball mill, DCP mill, an apex mill and a pearl mill; andmedia-free powdering machines such as Ultimizer (manufactured by SuginoMachine Ltd.), Nanomizer (manufactured by Nanomizer Inc.), Microfuldizer(manufactured by Mizuho Industrial Co., Ltd.) and DeBee 2000(manufactured by Debee Corporation). The toner particle in a liquiddeveloping agent obtained by wet pulverization preferably has an averageparticle diameter of 0.1 to 5 μm, more preferably 0.1 to 3 μm, from thepoint of obtaining a highly fine photographic image.

The liquid developing agent obtained from the materials and productionmethod described above is a liquid developing agent capable of realizinghigh solid content having excellent developing properties as well.

For example, in the liquid developing agent of the present invention,the solid content concentration in the liquid developing agent ispreferably 13 to 50% by mass based on the whole solid componentsincluding the pulverized powder of colored chip (i.e., toner particle),pigment dispersant, and other solid content. By using wet pulverizationmethod of colored chip being fundamentally difficult to maintaindispersion stability and charging characteristics, good flowability anddeveloping property can be maintained up to 50% by mass of solid contentconcentration, which can exhibit a nonconventional very great effect.

EXAMPLES

The liquid developing agent of the present invention will be describedin detail with reference to Examples below. Additionally, unlessotherwise noted, “part” and “%” mean “part by mass” and “% by mass”,respectively.

The pigment, pigment dispersant and thermoplastic resin used in thefollowing Examples and Comparative Examples are explained.

<Pigment>

Pigment blue 15:3 (manufactured by Dainichiseika Color & Chemicals Mfg.Co., Ltd.)

<Pigment Dispersant 1>

In a reactor was charged a mixture of 30 parts of an epoxy-modifiednovolak resin (manufactured by Japan Epoxy Resins Co., Ltd., Epicoat154), 75 parts of a polyester with an acid value of 30 andweight-average molecular weight of 4500 obtained by polycondensation of12-hydroxystearic acid, 35 parts of stearic acid and 0.2 parts oftetraethylammonium bromide, heated and stirred at 130 to 150° C. undernitrogen atmosphere for 3 hours, then the catalyst was removed by vacuumfiltration to give a modified novolak resin (pigment dispersant 1) witha weight-average molecular weight of 8000.

<Pigment Dispersant 2>

To a reactor were added 100 parts of 12-hydroxystearic acid, 10 parts ofxylene and 0.1 parts of tetra-n-butyl titanate, condensation reactionwas conducted at 180 to 200° C. while azeotropically distilling watergenerated out under nitrogen stream. Xylene was distilled out at apredetermined acid value, thereby to obtain a polyester of a light brownpolymer having an acid value of 33 and weight-average molecular weightof 4400. Next, 74.3 parts of this polyester and 25.7 parts of acopolymer of styrene and glycidyl methacrylate as an epoxy-containingcopolymer (respective contents; 80 mol % and 20 mol %) were reacted at130 to 150° C. in 40 parts of dimethylformamide as a solvent. From themeasurement of acid value and an epoxy group, the solvent was distilledout under reduced pressure when the residual amount of a carboxylic acidand an epoxy group was not more than measuring limit, thereby to give agraft copolymer (pigment dispersant 2). The weight-average molecularweight by GPC measurement was 35000.

<Comparative Pigment Dispersant>

As a comparative pigment dispersant, Solsparse 17000 (Abesia Co., Ltd.)was used.

<Thermoplastic Resin 1>

Epoxy resin (AER6064, manufactured by Asahi Kasei Corporation) was used.

<Thermoplastic Resin 2>

76.7 parts of styrene (St), 14.7 parts of stearyl methacrylate (SMA),8.6 parts of dimethylacrylamide (DMAA), 160 parts of toluene and 1.5parts of azobisisobutyronitrile as an initiator were mixed, radicalreaction was conducted at 80° C. for 10 hours. The resultant resinsolution was further heated at 150° C. for 8 hours under reducedpressure under the condition of 70 cmHg (about 93 kPa), toluene,unreacted monomers and low molecular oligomers were distilled out,thereby a thermoplastic resin 2 was obtained. The thermoplastic resin 2obtained had the composition (St:SMA:DMAA=85:5:10 mole ratio),weight-average molecular weight of 45800 and a melting point of 92° C.

Example 1

After cooling the milled product (colored chip) obtained by meltkneading of 250 parts of Pigment blue 15:3 and 750 parts ofthermoplastic resin 1 at 140° C. using a hot three-roll mill, it waspulverized using a jet mill (manufactured by Nippon Pneumatic Mfg. Co.,Ltd.). Next, 140 parts of this coarse pulverized powder, 8.8 parts ofpigment dispersant 1 and 551.2 parts of paraffin based solvent with ahigh boiling point (Moresco White P-40) were subjected to wetpulverization at 40° C. for about 90 minutes using Eiger mill (tradename M-250) filled with zirconia beads of 0.5 mm diameter, thereby togive a liquid developing agent 1 with a solid content concentration of21.3%.

Example 2

After cooling the milled product (colored chip) obtained by meltkneading of 250 parts of Pigment blue 15:3 and 750 parts ofthermoplastic resin 1 at 140° C. using a hot three-roll mill, it waspulverized using a jet mill (manufactured by Nippon Pneumatic Mfg. Co.,Ltd.). Next, 140 parts of this coarse pulverized powder, 5.3 parts ofpigment dispersant 1 and 554.7 parts of paraffin based solvent with ahigh boiling point (Moresco White P-40) were subjected to wetpulverization at 40° C. for about 90 minutes using Eiger mill (tradename M-250) filled with zirconia beads of 0.5 mm diameter, thereby togive a liquid developing agent 2 with a solid content concentration of20.8%.

Example 3

After cooling the milled product (colored chip) obtained by meltkneading of 333 parts of Pigment blue 15:3 and 667 parts ofthermoplastic resin 1 at 140° C. using a hot three-roll mill, it waspulverized using a jet mill (manufactured by Nippon Pneumatic Mfg. Co.,Ltd.). Next, 210 parts of this coarse pulverized powder, 5.3 parts ofpigment dispersant 1 and 484.7 parts of paraffin based solvent with ahigh boiling point (Moresco White P-40) were subjected to wetpulverization at 40° C. for about 90 minutes using Eiger mill (tradename M-250) filled with zirconia beads of 0.5 mm diameter, thereby togive a liquid developing agent 3 with a solid content concentration of30.8%.

Example 4

After cooling the milled product (colored chip) obtained by meltkneading of 250 parts of Pigment blue 15:3 and 750 parts ofthermoplastic resin 1 at 140° C. using a hot three-roll mill, it waspulverized using a jet mill (manufactured by Nippon Pneumatic Mfg. Co.,Ltd.). Next, 140 parts of this pulverized powder, 8.8 parts of pigmentdispersant 2 and 551.2 parts of paraffin based solvent with a highboiling point (Moresco White P-40) were subjected to wet pulverizationat 40° C. for about 90 minutes using Eiger mill (trade name M-250)filled with zirconia beads of 0.5 mm diameter, thereby to give a liquiddeveloping agent 4 with a solid content concentration of 21.3%.

Example 5

A liquid developing agent 5 with a solid content concentration of 21.3%was obtained in the same manner as in Example 1 except that thethermoplastic resin 2 in place of the thermoplastic resin 1, and aparaffin based solvent with a high boiling point (IP Solvent 2835) inplace of a paraffin based solvent with a high boiling point (MorescoWhite P-40) were used.

Comparative Example 1

After cooling the milled product (colored chip) obtained by meltkneading of 250 parts of Pigment blue 15:3 and 750 parts ofthermoplastic resin 1 at 140° C. using a hot three-roll mill, it waspulverized using a jet mill (manufactured by Nippon Pneumatic Mfg. Co.,Ltd.). Next, 140 parts of this coarse pulverized powder and 560 parts ofa paraffin based solvent with a high boiling point (Moresco White P-40)were subjected to wet pulverization at 40° C. for about 90 minutes usingEiger mill (trade name M-250) filled with zirconia beads of 0.5 mmdiameter, thereby a liquid developing agent 6 with a solid contentconcentration of 20% was obtained.

Comparative Example 2

After cooling the milled product (colored chip) obtained by meltkneading of 250 parts of Pigment blue 15:3 and 750 parts of thethermoplastic resin 1 at 140° C. using a hot three-roll mill, it waspulverized using a jet mill (manufactured by Nippon Pneumatic Mfg. Co.,Ltd.). Next, 140 parts of this coarse pulverized powder, 8.8 parts ofSolsperse 17000 (manufactured by Abecia Limited) and 551.2 parts of aparaffin based solvent with a high boiling point (Moresco White P-40)were subjected to wet pulverization at 40° C. for about 90 minutes usingEiger mill (trade name M-250) filled with zirconia beads of 0.5 mmdiameter, thereby a liquid developing agent 7 with a solid contentconcentration of 21.3% was obtained.

<Evaluation>

The liquid developing agents 1 to 7 prepared in Examples 1 to 5 andComparative Examples 1 to 2 were measured for a viscosity, an electricresistance value and a range of particle diameter. The results are shownin Table 1.

(Viscosity)

The viscosity of liquid developing agent at 25° C. was measured as aviscosity after 60 seconds using an E-type viscometer (at 20 rpm forviscosity not less than 10 mPa·s but less than 100 mPa·s; 5 rpm forviscosity more than 100 mPa·s). Additionally, the viscosity of liquiddeveloping agent of Comparative Example 1 was too high to measure.

(Electric Resistance Value)

The liquid developing agents (viscosity was able to be measured) weremeasured for an electric resistance value by a R834 manufactured byAdvance Corporation.

(Range of Particle Diameter)

The liquid developing agents were measured for the range of particlediameter of toner particles by eye using an optical microscope(manufactured by Olympus Corporation).

TABLE 1 Viscosity Volume resistivity Range of particle (mPa · s) (Ω ·cm) diameter (μm) Ex. 1 16 6.0 × 10¹³ 1-2 Ex. 2 20 3.0 × 10¹⁴ 1-2 Ex. 3100 5.0 × 10¹⁴ 1-2 Ex. 4 21 4.0 × 10¹³ 1-2 Ex. 5 50 5.0 × 10¹⁴ 1-2 Com.Ex. 1 — — >5 Com. Ex. 2 15 8.0 × 10¹² 1-4

INDUSTRIAL APPLICABILITY

A liquid developing agent obtained by wet pulverization of a coloredchip obtained by heat kneading a pigment with a thermoplastic resinusing a specific pigment dispersant having an aromatic ring and aring-opened structure of an epoxy group by a hydroxycarboxylicacid-derived carboxyl group has, in spite of wet pulverization method, alow viscosity being capable of realizing high solid content, further hasa high electric resistance value and excellent developing properties.

1. A liquid developing agent where a colored chip obtained by heatkneading a pigment with a thermoplastic resin is dispersed by wetpulverization in an electrically insulating hydrocarbon solventdissolving at least one pigment dispersant selected from the groupconsisting of the following modified novolak resin (A) and copolymer (B)having an aromatic ring and a ring-opened structure of an epoxy group bya hydroxycarboxylic acid-derived carboxyl group: Modified novolak resin(A): a modified novolak resin having a novolak resin-derived aromaticring and at least one group shown by a general formula (1) byring-opening of an epoxy group by a hydroxycarboxylic acid-derivedcarboxyl group:

wherein an oxygen atom at the far left is derived from an oxygen atomcontained in an aromatic hydroxyl group of a novolak resin, W¹ and X¹each independently represent a divalent hydrocarbon group with carbonnumbers of 1 to 19, i and j each independently represent an integer ofi=1 to 30 and j=0 to 30, and R¹ represents a hydrogen atom or a methylgroup. Copolymer (B): a copolymer with a weight-average molecular weightof 3000 to 100000, having, in said copolymer, the amount correspondingto at least 10 mol % of the recurring unit shown by a general formula(2), and the amount corresponding to at least 10 mol % of at least onekind selected from the recurring units shown by a general formula (3)and a general formula (4):

wherein W² and X² each independently represent a divalent hydrocarbongroup with carbon numbers of 1 to 19, p and q each independentlyrepresent an integer of p=1 to 30, and q=0 to 30, R², R³ and R⁴ eachindependently represent a hydrogen atom or a methyl group, R⁵ representsa hydrogen atom or a halogen atom, R⁶ and R⁷ each independentlyrepresent a hydrogen atom, a hydrocarbon group with carbon numbers of 1to 5, an alkoxy group with carbon numbers of 1 to 5, an aryloxy groupwith carbon numbers of 6 to 10, or a halogen atom, R⁸ represents ahydrogen atom or a methyl group, and R⁹ represents a direct bond or amethylene group.
 2. The liquid developing agent of claim 1, wherein theconcentration of the total solid content in a liquid developing agentwas 13 to 50% by mass.
 3. The liquid developing agent of claim 1,wherein the composition of the pigment dispersant is 2 to 100 parts bymass relative to 100 parts by mass of the colored chip.
 4. The liquiddeveloping agent of claim 1, wherein said electrically insulatinghydrocarbon solvent is a high boiling point paraffin solvent.
 5. Aprocess for producing the liquid developing agent of claim 1, whereinthe colored chip obtained by heat kneading a pigment with athermoplastic resin is subjected to dry pulverization into a coarsepulverized powder beforehand, further, said coarse pulverized powder issubjected to wet pulverization in an electrically insulating hydrocarbonsolvent dissolving at least one pigment dispersant selected from thegroup consisting of said modified novolak resin (A) and said copolymer(B).
 6. The liquid developing agent of claim 1, wherein theconcentration of the total solid content in a liquid developing agenthas 13 to 50% by mass, and wherein the composition of the pigmentdispersant is 2 to 100 parts by mass relative to 100 parts of mass ofthe colored chip.
 7. The liquid developing agent of claim 6, whereinsaid electrically insulating hydrocarbon solvent is a high boiling pointparaffin solvent.
 8. The liquid developing agent of claim 1, wherein thecomposition of the pigment dispersant is 2 to 100 parts by mass relativeto 100 parts by mass of the colored chip, and wherein said electricallyinsulating hydrocarbon solvent is a high boiling point paraffin solvent.